The more uncertainty they create with regards to opportunities to get keys, the more likely certain players are to buy deals that contain keys. If they said how many opportunities were left to get keys, people like myself would begin frantic calculations and cost-benefit analyses to determine whether or not it was worthwhile to continue trying to get keys. Denying players this information prevents them from doing the mental math and may force others into simply buying deals with keys in order to remove all uncertainty and be done with it.